From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx152.postini.com [74.125.245.152]) by kanga.kvack.org (Postfix) with SMTP id D60206B0006 for ; Wed, 10 Apr 2013 17:25:58 -0400 (EDT) Received: from /spool/local by e39.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 10 Apr 2013 15:25:58 -0600 Received: from d03relay02.boulder.ibm.com (d03relay02.boulder.ibm.com [9.17.195.227]) by d03dlp03.boulder.ibm.com (Postfix) with ESMTP id 3976919D8036 for ; Wed, 10 Apr 2013 15:25:49 -0600 (MDT) Received: from d03av01.boulder.ibm.com (d03av01.boulder.ibm.com [9.17.195.167]) by d03relay02.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r3ALPpEJ131392 for ; Wed, 10 Apr 2013 15:25:52 -0600 Received: from d03av01.boulder.ibm.com (loopback [127.0.0.1]) by d03av01.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id r3ALPpxM018092 for ; Wed, 10 Apr 2013 15:25:51 -0600 Message-ID: <5165D8DE.5090801@linux.vnet.ibm.com> Date: Wed, 10 Apr 2013 14:25:50 -0700 From: Cody P Schafer MIME-Version: 1.0 Subject: Re: [PATCH v3 00/11] mm: fixup changers of per cpu pageset's ->high and ->batch References: <1365618219-17154-1-git-send-email-cody@linux.vnet.ibm.com> <20130410142354.6044338fd68ff2ad165b1bc8@linux-foundation.org> In-Reply-To: <20130410142354.6044338fd68ff2ad165b1bc8@linux-foundation.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Gilad Ben-Yossef , Simon Jeons , KOSAKI Motohiro , Mel Gorman , Linux MM , LKML On 04/10/2013 02:23 PM, Andrew Morton wrote: > On Wed, 10 Apr 2013 11:23:28 -0700 Cody P Schafer wrote: > >> "Problems" with the current code: >> 1. there is a lack of synchronization in setting ->high and ->batch in >> percpu_pagelist_fraction_sysctl_handler() >> 2. stop_machine() in zone_pcp_update() is unnecissary. >> 3. zone_pcp_update() does not consider the case where percpu_pagelist_fraction is non-zero >> >> To fix: >> 1. add memory barriers, a safe ->batch value, an update side mutex when >> updating ->high and ->batch, and use ACCESS_ONCE() for ->batch users that >> expect a stable value. >> 2. avoid draining pages in zone_pcp_update(), rely upon the memory barriers added to fix #1 >> 3. factor out quite a few functions, and then call the appropriate one. >> >> Note that it results in a change to the behavior of zone_pcp_update(), which is >> used by memory_hotplug. I'm rather certain that I've diserned (and preserved) >> the essential behavior (changing ->high and ->batch), and only eliminated >> unneeded actions (draining the per cpu pages), but this may not be the case. >> >> Further note that the draining of pages that previously took place in >> zone_pcp_update() occured after repeated draining when attempting to offline a >> page, and after the offline has "succeeded". It appears that the draining was >> added to zone_pcp_update() to avoid refactoring setup_pageset() into 2 >> funtions. > > There hasn't been a ton of review activity for this patchset :( > > I'm inclined to duck it until after 3.9. Do the patches fix any > noticeably bad userspace behavior? No, all the bugs are theoretical. Waiting should be fine. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org